The field of this invention is turbo machine blading and methods. More particularly, this invention relates to fluid energy reactive blading for a rotatable blade wheel of a combustion turbine engine.
The most pertinent conventional turbo machine blading known to the applicant is illustrated in U.S. Pat. Nos. 2,971,743; 3,185,441; and 3,479,009. Because the last of these patents is perhaps the most relevant to this invention, a brief discussion of the blading illustrated by this patent follows in order to afford the reader with an understanding of a few of the deficiencies of conventional turbo machine blading.
Upon examination of the turbo machine blading illustrated in U.S. Pat. No. 3,479,009, it will be noted that each of the blades includes a circumferentially extending shroud section which is generally S-shaped to define axially and radially extending curvilinear abutment surfaces. The abutment surfaces of each shroud section interlock with the matching abutment surfaces of next adjacent blades so that a substantially continuous shroud is defined by the interlocking shroud sections. Because the curvilinear abutment surfaces of the shroud sections extend axially, a radial projection of these shroud surfaces toward the axis of blade wheel rotation intersects with the platform or base of the respective blades. Consequently, when these abutment surfaces are formed during manufacture of a blade, the forming tool must be advanced to form the abutment surfaces and then be retracted before the tool engages and damages the blade platform. For example, if the curvilinear abutment surfaces are formed by the use of a grinding wheel dressed to a matching shape, the grinding wheel must be passed radially inwardly relative to the shroud section to generate the abutment surfaces thereon, be stopped, and then be retracted radially outwardly. Such an advance-stop-retract type of machining operation is time consuming and costly. Thus, because turbo machines usually contain many blades, the cost of machining the blading can be a significant portion of the total manufacturing cost for the turbo machine. Further, such a machining operation has the potential for damaging a blade if the machining tool is advanced too far and cuts into the blade platform.
A further aspect of manufacturing conventional turbo machinery blading involves obtaining a reference position of a blade preparatory to performing machining operations on the blade. Conventionally, a fixture is used which supports the blade, at least in part, by engaging the airfoil or bucket portion of the blade. The blade may additionally be supported by the fixture engaging another portion of the blade. For example, the fixture may also engage the platform portion of the blade. In any case, fixturing which engages the airfoil or bucket portion of a blade is necessarily complex and expensive because of the complex nature of the airfoil or bucket surface which the fixture must engage. Additionally, this type of fixture may damage the airfoil or bucket portion of a blade so that the blade must be scrapped.